Method of casting die sets



June 5, 1951 E. SCHAEFER METHOD OF CASTING DIE SETS Fi1 d t. 5, 1945 IN VEN TOR.

Edward Schaefer BY llll 1am.

orrggs Patented June 5, 1951 METHOD OF CASTING DIE SETS Edward Schaefer, Williamsville, N. Y., assignor to Arthur E. Petzon, Buffalo, N. Y.

Application October 5, 1945, Serial No. 620,454

2 Claims.

This invention relates to dies of the kind used in various punching and stamping operations and particularly to a novel method of producing the same.

According to the present diemaking practice, the diemaker generally purchases a die set consisting of a cast iron or steel die shoe and a cast iron or steel punch holder as a catalog item from suppliers of standard die sets. The supplier of die sets provides a die shoe and punch holder with related guide pins and guide bushings and the punch holder is usually provided with an upwardly extending shank for securement in the ram or slide of a punch press. The machining operations of the die set comprise mainly the finishing of the upper and lower surfaces of the die shoe and punch holder and fitting of the guide pins and guide bushings therein. These operations are accomplished in accordance with regular machine shop practice.

In die sets produced in the conventionalmanner die shoes and punch holders of the same specification and catalog number are not generally speaking interchangeable due to the necessary manufacturing tolerances. Further, die sets of theconventional kind, being of cast iron or steel, generally exceed in weight the actual dies, punches and other appurtenances which the die maker fabricates and secures to the die shoe and punch holder respectively.

The diemaker, in building a die, starts with the purchased cast iron or cast steel die set and machines the punch holder and die shoe to provide suitable recesses for receiving the die and the punch and for fastening the die and punch to the die shoe and punch holder, usually by means of screws or the like. All of these steps in fabrication must be carried on according to usual machine shop practices and in the usual rather slow and laborious manner in which normal non-production machine tool operations are performed on ferrous metals.

We have constructed a die set wherein the main body portions of the die shoe and punch holder are formed of thermoplastic resin with the guide pins and guide bushings and any other desired metal parts cast in situ. Die sets so constructed are accurate beyond any degree of precision which is commonly practical in the production of all metal die shoes and punch holders and to a degree where full interchangeability of die shoes and punch holders of a given style and catalog number are feasible. In fact, by use of the die sets of the present invention, varying die shoes and punch holders may be interchangeably used in sets as long as the diameter and spacing of the guide pins and the guide bushings are the same. Thus varying styles of punch holders may be used with a given die shoe as special cases may dictate.

The guide pins and guide bushings are preferably undercut where they are embedded in the die shoe and punch holder, respectively, so that they cannot he accidentally dislodged, and the necessity for producing the usual drive fit of guide pins and guide bushings is eliminated.

The facility with which resin articles are provided in a wide variety of colors makes it possible, according to the present invention, to furnish die sets in a variety of colors. This possibility makes it practical for a manufacturer to use the color factor in distinguishing classes or groups of dies. For instance, all of the dies for producing parts for a particular model of a product may be of one color while the dies for another model may be of a contrasting and readily distinguishable color, so that identification and classification of a die to that extent may instantly be made.

A die set constructed according to the present invention is illustrated in detail in the accompanying drawing and is described in the following specification. This disclosure is by way of example only and to illustrate the principles of the present invention. The scope of the invention is not limited to a die set of the form shown and described or in any other way excepting as defined in the appended claims.

In the drawing:

Fig. l is a top plan view of one form of "the die set of the present invention;

Fig. 2 is a cross-sectional view on the line 2-2 of Fig. 1;

Fig. 3 is a detailed perspective view of a guide bushing-for the punch holder of the die set of Figs. 1 and 2;

Fig. 4 is a perspective view of a guide pin for the die shoe of the die set of Figs. 1 and 2; and

Fig. 5 is a perspective view of one of the reinforcing rings associated with the shank of the punch holder of Figs. 1 and 2.

In the several figures of the drawing, like characters of reference denote like parts and the numeral l0 designates a die shoe and the numeral H designates a punch holder. The die shoe and punch holder are of a very well-known and conventional form and configuration and are merely representative of a wide variety of conventional die shoes and punch holders which may be produced according to the present invention.

In the die set illustrated by way of example die shoe Ill has a pair of vertically extending guide pins l2, each of which is helically undercut as at I3 to embed the guide pins in the die shoe at the time the plastic material of which the die shoe is formed is cast or molded. To further reduce the weight of the die set to a minimum guide pins l2 may be of tubular form as illustrated. In a similiar manner, complementary guide bushings [4 are fixed in the punch holder 1 I when the punch holder is molded or cast'and the guide bushings M are likewise provided with helical undercuts IE to prevent accidental removal of the guide bushings. Other irregular or stepped formations or enlargements or other anchoring devices may be substituted forthe undercutting of either the guide pins or the bushings.

In the preferred method of producing the die set of the present invention the'molding 'die is used having two cavities, one for the die shoe and one for the punch holder, with means for supporting each guide pin and its guide bushing in assembled relation. The cavities will thus necessarily be positioned relatively just as the die shoe and punch holder are positioned when assembled, although their spacing in the mold mayv vary within certain limits. This method of manufacture absolutely insures proper'fit ofthe guide pins and bushings and produces a complete die set ineach molding or casting operation.

While various organic plastic materials may be employed, we have found that highly satisfactory results'are attained with a thermo-plastic resin marketed by the Dow Chemical Company under the brand name Ethocel 'I. F. This product is available in varying degrees of hardness and Ethocel 4.00 or Ethocel 500 are both highly suitable. These resins are ethyl ethers of cellulose. It is to be understood that reference to one specific organic plastic is by way of example only and that any other material having similar pliysi cal properties may be used without departing from the spirit of the present invention.

In the illustrated instance, the punch holder H has a shank 11 formed integrally therewith and of the same plastic material. As shown in Fig.2, a pair of annular metal reinforcing rings l8 are assembled upon shank ll by being placed in' position in the mold before the punch holder is cast or molded. The use of such ring is optional.

Plastic molds or plastic molding dies by their nature produce highly precise duplicate molded products so that a master mold comprising a cavity for the die shoe and a cavity for the punch holder will automatically produce highly precise duplicate die shoes'and punch holders with the guide pins and guide bushings highly precisely that the set illustrated will be suitably 'Inachined and drilled to receive and have secured thereto proper die and punch elements and conventional gauges and stops and stripping means.

However, such machining is only the special machining required on the part of the diemaker in any event, and no machining prior to delivery of the finished die set to the diemaker is required on the part of the die set manufacturer. In producing blanking dies the die shoe is also usually provided with an opening therethrough to permit blanks to pass downwardly through the die shoe. These fabricating steps performed by the diemaker can be accomplished with much greater efficacy on conventional thermo-plastic resin, commonly called plastic, than on iron or steel die shoes and punch holders. We have found that the structural strength of conventional thermo-setting resins of the general type referred to above is entirely adequate for dies of all usual designs and capacities, particularly since the stresses normally exerted upon die shoes and punch holders is mainly purely compressive.

The higher cost per pound of the resin used in the present invention, as compared with iron or steel,- is partly offset by its much lighter weight per die set, and is further canceled out by reason of the ease with which the material of die shoes" v 1. The method of producing die sets comprisins positioning a pair of slidably telescoping guide pins and a pair of guide bushings in assembled relation with a portion of each guide pin projecting from its bushing and with the pair of pin and bushing assemblies in spaced parallel relation, casting an organic plastic die shoe jointly about the projecting portions of the guide pins, and casting an entirely separate organic plastic punch holder jointly about the guide bushings.

2. The method of producing die sets comprising positioning a plurality of slidably telescoping guide pins and bushin s in assembled relation with a portion of; each guide pin projecting from its bushing and with the several pin and bushing assemblies inspaced parallel relation, casting an organic plastic slabjointly about the projecting portions of the several guide pins, and casting an entirely separate organic plastic slab jointly about the several guidebushingspone of' said slabs comprising a die shoe and the other of said slabs comprising a punch holder.

EDWARD SCHAEFER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,997,500 Swarovsky Apr. 9, 1935 2,085,959 Donegan July 6, 1937 2,186,799 'Boker Jan. 9, 1940 2,238,302 Baumbach Apr. 5, 1941 2,242,117 English May 13, 1941 2,370,836 Benedetto Mar. 6, 1945 2,392,804 Basolo Jan. 15, 1946 

